1. Field of the Invention
The invention relates to a dot impact type printing head and, more particularly, to a dot impact type printing head provided with a plurality of print units having piezoelectric elements extended with application of a voltage.
2. Description of the Related Art
A dot impact type printing head having a plurality of print units is disclosed in Japanese Pat. Laid-Open Publication No. 63-312852. Each of the print units includes a piezoelectric element where a plurality of piezoelectric ceramics are bonded to each other in a laminated state, an extension transmitting mechanism for enlarging the extension of the piezoelectric element to drive a print wire, and a support frame for supporting the extension transmitting mechanism and the piezoelectric element. The plurality of print units are arranged radially inside the printing head. A first board is disposed at the rear end of the printing head, and a second board is disposed at the fore end of the printing head. The support frame of each print unit is secured to the first board by a bolt fastened in the longitudinal direction of the print unit, i.e., in the direction of the extension of the piezoelectric element. The support frame of each print unit is fixed to the second board by a bolt fastened in the direction perpendicular to the longitudinal direction of the print unit.
However, there is a possibility of generation of a longitudinal dimensional error in the support frame of the print unit or of manufacture error in flatness at the end surfaces of the first and second boards in contact with the support frame. Furthermore, variation in the fastening force may be generated in the bolt fastening operation. Therefore, deformation in the support frame may be caused in the above-mentioned printing head where both fore and rear ends of the support frame are fastened by the bolts. If the support frame is deformed to be extended in the longitudinal direction, the extension of the piezoelectric element is not exactly transmitted to the extension transmitting mechanism, thus reducing the impact force of the print wire. Moreover, in assembling the printing head, the support frame of each print unit must be fastened twice by the bolts, which is cumbersome and time consuming.